I Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July 1983 Buffet maneuver vibration energy is concentrated in the low frequency range, typioally between 20 to 100 Hz, dominated by the store~s structural charac- teristic. Depending upon the store location on the aircraft and configuration on the rack, pylon, and aircraft,,additional distinct responses may be pre- dominant in the store response. Due to these factors, vibration levels should be derived from in-flight vibration measurement. The maneuver buffet and aero- dymmic vibration tests may be combined or performed separately.
For stores that are deployed by separation from the aircraft (free flight) such as bombs and missiles, a free-flight functional test is recommended when the free-flight vibration amplitude is greater than the captive-flight levels. In general, if the free-flight dynamic pressure is greater than the captive-flight levels it can be assumed that the associated vibration level will also be higher. In this case if measured free-flight data does not exiet, the factors Al and A2 from table 514.3-VI should be set equal to one. The value of q should be the maximum value attainable during free flight.
The duration of this functional test, per axis, should equal the maximum free-flight time expected at maximum vibration levels. a. ~a: The test levels and spectrum for the three vibration environments, captive flight, free-flight, and buffet, can be selected from table 514.3-VI and fiugres 514.3-30, 31, and 32. The use of these tables and figures is suggested only when there is an absence of satisfactory flight measurements. b. ~. The test duration should be developed from flight measurements, flight characteristics, and flight durations utilizing appendix A.
If this data is not available, then test durations can be obtained from the information giv~n in paragraphs 1-4.3, I-4.6, I-4.7, I-4.8 and 1-4.9. 0 c. $sst set~. Suspend the store from a structural frame by means of its normal mounting luge hooks and sway braces which simulate the operational mounting apparatus. The test setup shall be such that the rigid body modes (translationand rotation) or vibration for the store/frame/suspeneion system are between 5 and 20 Hz. Vibration shall be applied to the store by means of a rod or,other suitable mounting device running from a vibration shaker to a relatively hard, structurally supported point on the surface of the store.
Alternatively, the store may be hard-mounted directly to the shaker, using its normal mounting lugs and a suitable fixture. The stiffness of the mounting fixture shall be such that its induced resonant frequencies are as high as possible but none are below one-third of any f. frequency. For both methods, launcher rails shall be used as part of the test setup, where applicable. Accelerometers to monitor the vibratory respon’seof the store should be mounted on two relatively hard pointa or rings within the store, one in the nose section and one in the aft section. For atores such as bombe with nonintegral tail cones, the aft-section mounting point should be in the aftmost section of ..
the main body of the store. At each mounting point or ring, two accelerometers should be mounted--one in the vertical and one in the lateral plan. (Longi- tudinal direction is along the axis of the store, the defined as perpendicular to the longitudinal axis and pasaing through the mOuntinS lugs). vertical direction is contained in a plane o METHOD 514.3 19 July 1983 514.3-46